The installation of pylon spires of South Africa’s Msikaba Bridge is well underway. Soon, the spires are expected to tower 130 meters high on each side of the 200 meters deep river gorge. According to Laurence Savage, this momentous phase will reveal the “sheer grace of the design of the bridge in addition to the awesome scale of the development.” Savage is Concor’s Project Director on this contract.
The spires are being slip-formed from the bifurcated legs of the elegant inverted Y-shape concrete pylons that will become a hallmark of this iconic structure. Each tower rests on two inclined legs that meet 21 meters from the start of the bifurcation which extends a full 11 meters.
At 32 meters, the first section of the spire (starting with a diameter of six meters) is uninterrupted for 55.7 meters and comprises 14 slip-form lifts. The inclusion of 17 anchor inserts begins over the next 35 meters of the spire, which reaches a height of 124 meters and will have converged to a four-meter diameter.
These anchor inserts accommodate the 17 cables that run from the anchor blocks located behind each pylon to the spire, and then down to the 580 m-long bridge deck.
The installation process of the pylon spires on South Africa’s Msikaba Bridge
To accomplish the lifts, Savage explained that they are using a jacking system for the formwork shutters, with eight jacks around the circumference of the spire. “Each lift, he continued, is 3.6M conducted at intervals of about two weeks per lift. We are making steady progress and we are also paying attention to quality and safety.”
With regard to the latter, the work is accessed using a specialized stair system. One set of access stairs is set from ground level to the top of the bifurcation and a second one follows the shutter system up the spire. The formwork system comprises three decks that trail below each other and that lift together as the shutters are jacked up.
According to the Concor’s Project Director on this contract, the depth of the gorge is around 197 meters, therefore, no work on the bridge deck itself can be done from ground level. Everything has to be done suspended from the two pylons, one on the south side of the gorge and the other on the north side of the river.